13 Benefits of the Marimo Moss Ball

Live plants are very beneficial for aquariums. They do everything from absorb toxic nitrates to give your animals a natural, beautiful environment to live in. Unfortunately, not all of us have green thumbs. Over the years, I have struggled to keep live plants in my aquariums, even easy ones like Anacharis and Jungle Val, both of which have died on me.

So what’s one to do? Out of all the live plants I have had in my aquariums, there is one plant (well, sort of plant) that has not failed me: the Marimo moss ball.

The moss ball is not to be confused with cheap knockoffs (Java wrapped around plastic or foam spheres). Instead, Marimo moss balls are little squishy balls of algae that look a lot like moss, hence the name. In the wild, they roll along the bottoms of rivers, giving them their round shape. They are also viewed as charms in Japan, and even treated as pets.

Aside from its unique appearance, here are some benefits of having a Marimo moss ball in your aquarium.

1. Sucks Up Nitrates and Other Nasties

Byproducts of fish waste, nitrates are harmless to most healthy fish under 30ppm, but as their numbers increase over time, they can stress and kill your fish. Partial water changes are performed to keep nitrates in check.

Like live plants, moss balls absorb nitrates. But—also like plants—it’s usually not a large amount. The ball would make a difference only if it were kept in just a few gallons of water. Still, any nitrate absorbent is a benefit to your tank’s ecosystem. Moss balls are also like little filters, sucking up debris and small amounts of ammonia and phosphates.

2. Provides Some Oxygen

Like plants in general, moss balls suck up CO2 and release oxygen in the water. If you don’t like noisy air stones, some Marimo moss balls are a great addition to help you oxygenate your tank.

3. Helps Prevent Excess Algae Growth

What better way to combat algae than with algae? Marimo moss balls suck up the same nutrients as undesirable algae, depriving invasive algae of those nutrients. I had brown algae growing in my 10-gallon tank, but since wiping them off the glass and adding a few moss balls, they have yet to grow back. Of course, moss balls won’t make that much of an impact in larger aquariums unless you get more a lot of them. I don’t know about killing off algae, but they can help prevent unwanted algae from growing back.

4. Harbors a Good Amount of Beneficial Bacteria

While gravel and filter media is the most valuable seeding items for a new tank, the Marimo moss ball, like many plants, has colonized beneficial bacteria on its surfaces, and can make for great seeding material. I wouldn’t put one in a filter (in fear of hurting the moss ball) but they can help with the nitrogen cycle.

5. Requires Almost Zero Maintenance

The moss ball requires freshwater, some amount of lighting (prefers shading in bright tanks) and waste to feed off of. So basically, as long as you have an aquarium set up with aquatic animals, you’ve already got everything the algae ball needs. Every time you feed your fish, you are also feeding the moss ball, so no fertilizers are required.

There is only one task that must be done for a Marimo: it needs to be squeezed outside of the tank every once in a while. Yes, you should actually squeeze it (as you can’t do with the cheap Java knockoffs).

The Marimo sucks up a lot of filth and debris over time (like a sponge), which is a good thing. But it also absorbs more than it can chew, and the nasty stuff eventually leeches out. So every time you perform a partial water change, just remember to take out the moss ball, squeeze it over a bucket or sink, and toss it right back into the tank. It will float at the surface for a while unless you squeeze it again while underwater. Floating does not hurt the Marimo. In fact, the balls can float up to the surface on their own from internal gasses, as well as sink on their own.

There is technically another task for the moss ball: it should be moved around once in a while to keep its rounded shape, as well as to provide some lighting on every surface to avoid dead patches. But if you are performing routine gravel cleanings and squeezing the moss ball every week or two, then you’re accomplishing this anyway.

So yeah, squeezing the ball once in a great while is the only maintenance required.

6. Easily Adapts to High pH

A lot of aquarium plants don’t do so well in high pH water, but this doesn’t affect moss balls. I have kept moss balls in pH of 8.4, and they remained healthy.

7. Is Beloved By Shrimp (and Other Creatures)

Because the moss ball collects debris and nutrients over time, small freshwater shrimp enjoy scavenging through the green stuff and munching on any particles to their liking. I have also seen African Dwarf frogs lying on top or snuggling underneath the moss ball. Floating moss balls can even serve as toys for betta fish since they like moving the ball around. All in all, critters can use this ball of algae as a smorgasbord, a comfy hiding place, or a means of entertainment.

8. Is Snail-Proof

Some snails like to munch on live plants, resulting in dead organic matter that needs tossing out. Fortunately, they don’t harm the moss ball. I have had mystery snails, Malaysian Trumpets, Ramshorns, Zebras, and pond snails, and none of them damaged the Marimo. Snails sometimes nibble on the moss ball, eating food off of it like shrimp.

9. Does Not Produce Dead Matter

Lots of plants grow new leaves and lose old ones simultaneously—that's the sign of a healthy plant. But this also means having to remove the decaying parts of the plant from time to time, unless you want your nitrates to go up. No such maintenance for the Marimo! As long as they are healthy, moss balls stay green and intact.

10. Tolerates Salt Well

Aquatic plants don't do so well with salt. Freshwater aquarium salt can be used to treat various injuries and parasitic outbreaks, as well as keep nitrites down during mini cycles. Salt can actually benefit moss balls, as they are known to live in brackish water.

11. Does Not Bring Hitchhikers With It Into the Tank

When buying live plants from the fish store, you're often buying other creatures with it, from pond snails to tiny creatures not visible to the eye (such as parasites). Luckily moss balls are, for the most part, sold in individual cups. This minimizes the chance of unwanted residences in your fish tank.

12. Doesn't Need to Be Anchored

This is probably one of my favorite benefits of the moss ball, aside from the incredibly low maintenance. A lot of plants need to be anchored, by either burying their roots in gravel or tying them to an object until it attaches itself (which takes patience). It can be a chore removing anchored plants in order to clean the gravel. I would remove my Java Fern and afterward try to bury it again, which often took a few tries because I have a thin layer of gravel. While struggling to bury all the roots, some small amounts of debris would kick up and that would be really frustrating. It got to the point that I’d just avoid repositioning by vacuuming around it.

The moss ball isn’t meant to be anchored. It doesn’t need to be removed when cleaning gravel. It can merely be pushed aside by the siphon with no damage, and it’s one of the few items I don’t have to remove in order to do a thorough clean.

13. Almost Impossible to Kill

The only way to kill a Marimo is if you place it in water full of chlorine (such as untreated tap water), saltwater, or a cesspool (where there are no nutrients in the waste).

In other words, as long as you keep up with your maintenance on the tank, providing nutritious food for your animals, the moss ball will thrive. Remember that they prefer dim lighting. White specks on them indicate over-exposure to light. If they have brown patches and/or float up on their own, this means they are not getting enough light (a problem I've never had with them).

1. It Doesn't Affect Large Tank Health

While it has the same benefits as plants like absorbing nitrates and providing oxygen, the moss ball does these things on a smaller scale, at least compared to the bigger plants out there. To make a large dent on nitrates, oxygen levels, and the prevention of algae, tanks often have more than just a few plants when we get into double-digit gallons. Often a tank is filled with different species of plants to make a significant impact on tank levels.

To do this with the Marimo, you’d have to fill 1/4 of the tank with moss balls, and that would just look odd. That or have a moss ball the size of a bowling ball.

So if you only want algae or nitrate control (while the moss ball can contribute), you’d have to buy plants in addition. The Marimo just helps with these problems; it doesn’t solve them on its own. So don’t think a single moss ball in a 20 gallon is going to make a significant impact on your tank.

2. Goldfish Eat It

Goldfish are known to eat anything in their paths, so don’t be surprised if your goldfish tears this ball to shreds.

3. It Is Slow-Growing

The Marimo moss ball is the slowest growing plant I’ve ever seen. I’ve heard they can get to be the size of softballs or even bigger, but it takes years (closer to decades) with an enriched environment to get to that size. So if you want a larger ball, you’re in for a wait. If a moss ball is too big, they can be torn apart, resulting in smaller moss balls. You’ll have to regularly move them to make those irregular bits round again.

Of course, this means if you love the size of your moss ball, it will stay that size for a long time.

4. It Does Not Reproduce

While aquatic plants spawn over time, Moss balls won’t reproduce in your tank—they just get bigger. So you won’t find little baby moss balls or patches of the algae. This can be good or bad depending on what you want. Only tearing one apart will result in more moss balls, but I'd suggest just buying more. It can be years until a baby moss ball grows to golf ball size.

Overall this is a great little plant substitute for those of us who have difficulty with aquatic plants. I suggest having more than one in a tank if you want those benefits that plants have. If you want moss balls purely for decoration or as an addition to plant life, they are safe, fool-proof organisms that can only benefit your tank.